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GEOMATRIX <br /> ' concentration of 720 µg/l. No TPHg was detected in the grab groundwater samples collected <br /> from the two sampling locations downgradient of the affected soil. TPHd was detected in the <br /> ' grab groundwater sample collected from GB-1 (520µg/1) and in the unfiltered duplicate sample <br /> collected from GB-2 (140 µg/1). <br /> ' Review of the chromatograms indicates that the gasoline-range (TPHg) and diesel-range <br /> ' (TPHd) "detections", and possibly the detected PAHs, in the sample from GB-1 are caused by <br /> petroleum-affected soil particulates(<0.7 microns in size for TPHd analysis) entrained in the <br /> ' sample and are not representative of dissolved petroleum in groundwater. This is substantiated <br /> by the similar chromatogram pattern of both the soil sample and grab groundwater sample <br /> ' collected from GB-1. Groundwater analytical results are summarized in Table 2. Copies of the <br /> laboratory analytical reports, chain-of-custody records, and chromatograms are presented in <br /> Appendix B for both soil and groundwater analysis. <br /> ' 5.0 CONCLUSIONS ABOUT SITE STATUS AND RECOMMENDATIONS <br /> ' The purpose of the work described herein was to collect data to satisfy the requirements of the <br /> Technical Approach. Sufficient data now exist to conclude that the lateral and vertical extent of <br /> ' petroleum hydrocarbon-affected soil has been constrained.Benzene was not detected in any of <br /> the soil or grab groundwater samples; toluene, ethylbenzene, xylenes, and PAHs were detected <br /> ' at low concentrations in some of the soil and grab groundwater samples. <br /> ' The potential risk posed by toluene, ethylbenzene,xylenes, and the detected PAHs in soil at the <br /> site was evaluated based on a comparison to United States Environmental Protection Agency <br /> ' (U.S. EPA) Region IX Preliminary Remediation Goals (DRGs). PRGs are media-specific <br /> concentrations that are based on defined levels of carcinogenic or noncarcinogenic risk for a <br /> ' specific exposure scenario. U.S. EPA Region IX has developed PRGs for residential soil based <br /> on an excess cancer risk of one-in-one million(1x10`) or a hazard index for noncarcinogenic <br /> ' risk of 1 (U.S. EPA Region IX, 1998). As shown in Table 3,the concentrations of toluene, <br /> ethylbenzene, xylenes, and PAHs are several orders of magnitude less than their respective <br /> PRGs,indicating that the presence of these constituents in soil at the site, including the <br /> \\sf2\deptdata\Doc Sak\4780\.surldtpt.doc 5 <br />